Device for anchor testing



9, 1966 L. J. TRENKENSHUH 3,264,867

DEVICE FOR ANCHOR TESTING Filed NOV. 12, 1963 v 2 Sheets-Sheet 2 INVENTOR. L EON/4RD J TRENKE/VSHUH United States Patent Leonard The present invention relates to mine rock bolts used for reinforcing and supporting roofs of mines, and in particular a testing machine for determining the tensile strength required of rock bolts, making it possible to maintain the roof of a mine in good condition so that the possibility of failure of a mine roof or part of a roof is substantially obviated.

The purpose of this invention is to accurately determine anchor or breaking strengths of mine rock bolts by simulating conditions under which mine roof reinforcing or rock bolts function in a testing laboratory so that tensile or breaking strengths of rock bolts in mine roofs are readily determined.

The use of bolts, instead of supporting timbers, to hold mine roofs is well known. The bolts are inserted in holes that have been drilled upwardly into the roof of the mine and the upper ends are expanded to anchor the bolts in place. The bolts are adjusted or tightened to bolt the various strata of the roof together to provide a strong beam. Nevertheless, in time the strata may start to separate with the result that excessive loads may be applied to the bolts, and such loads may cause the bolts to stretch or fail. Upon failure of the bolts the roof will collapse, and in such instances the roof collapses without warning.

Where mine roofs require support to supplement inherent stability usually rigid plates are secured by bolts to the under surface of the roof, with the bolts extending upwardly two or ten feet. The bolts are anchored to superjacent earth or rock strata with their entire length except for a protruding head and the head is substantially enclosed within counterbores.

As is obvious too much torque or the tension vector resulting therefrom may weaken the bolt and foreshado-w its failure, or cause rupture of the rock surrounding the shell; while too little may be insufficient to lock the shell securely in the bore, or to draw the roof plate tightly against the under surface of the roof. It is apparent that unless the correct amount of tension stress is applied to the bolt the heavy roof plate may at any unpredictable moment drop and injure operators below.

With these thoughts in mind this invention contemplates an assembly similar to that existing in a mine whereby mine rock bolts may be subjected to stresses and strains similar to conventional stresses and strains of rock bolts in mine roofs, in a testing laboratory so that rock bolts of a mine roof may be adjusted to compensate for changing conditions in the strata of the roof.

The object of this invention is, therefore, to provide a mine rock bolt anchor ortester for determining torque and other stresses and strains of rock bolts in use.

Another object of the invention is to provide a mine rock bolt tester in which the anchoring means of expanding elements of the bolt are retained in a refractory material to simulate rock strata in the roof of a mine.

Another important object of the invention is toprovide an improved mine rock bolt anchor for laboratory use in which a refractory material is retained in a split sleeve in a shell so that the parts may be readily taken apart, and also readily assembled.

A further object of the invention is to provide a mine rock bolt testing construction which makes it possible to simulate a mine roof bolt condition in a laboratory.

A still further object of the invention is to provide a mine roof rock bolt testing apparatus by which loads on rock bolts in roofs of mines may be maintained constant.

And a still further object is to provide mine rock bolt testing means in which the testing means is of simple and economical construction.

Other and further objects and advantages of the present invention will be apparent from the following detailed description, drawings and claims, the scope of the invention not being limited to the drawings themselves as the drawings are only for the purpose of illustrating a method by which the principles of this invention can be applied.

Other embodiments of the invention utilizing the same or equivalent principles may be used and structural changes may be made as desired by those skilled in the art without departing from the present invention and the purview of the appended claims.

In the drawings:

FIGURE 1 is a front elevational view illustrating the improved mine rock bolt testing apparatus showing a wedge positioned in gripping elements on the upper threaded end of a rock bolt in a refractory material, simulating a section through mine roof strata, and with the parts positioned in a casing on an upper stationary cross-head with the rock bolt extended through and secured in a lower movable cross-head.

FIGURE 2 is a plan view of the mine rock bolt testing apparatus with the parts as shown in FIGURE 1, and with a bearing plate and supporting bolts shown in broken lines.

FIGURE 3 is an exploded view showing an outer casing, split sleeve, and an element of refractory material, the parts being shown in perspective.

While one embodiment of the invention is illustrated in the above-referred-to drawings, it is to be understood that they are merely for the purpose of illustration and that various changes in construction may be resorted to in the course of manufacture in order that the invention may be utilized to the best advantage according to circumstances which may arise, without in any manner departing from the spirit and intention of the device, which is to be limited only in accordance with the appended claims. And while there is stated the primary field of utility of the invention it remains obvious that it may be employed in any other capacity wherein it may be found applicable.

In the accompanying drawings, and in the following specification, the same reference characters are used to designate the same parts and elements throughout, and in which the numeral It) refers to the invention in its entirety, numeral 12 indicating a mine rock bolt, numeral '14 indicating a wedge at the upper end of the bolt, numeral 16 indicating an outer casing, numerals 18 and 20 indicating segments of a split sleeve in the casing 16 numeral 22 indicating a refractory material in the sleeve and positioned around the wedge and gripping elements 24, numeral 26 indicating an upper stationary cross-head, and numeral 28 a lower movable cross-head.

The outer casing 16, segments 18 and 20, and refractory 22 are positioned on a bearing plate 30 on the upper cross-head 26, and the lower end or head 32 of the rock bolt 12 is positioned below the lower movable cross-head 28. A washer 34 is positioned between the head 32 and a mine roof plate 36, and a lower bearing plate 38 is positioned between the plate 36 and lower surface 40 of the lower cross-head 28.

The mine rock bolt 12 extends through an opening 42 in the upper bearing plate 30, an opening 44 in the crosshead 26, an opening 4-6 in the cross-head 28, an opening 48 in the lower bearing plate 38, and an opening 56 in the mine roof plate 36.

The stationary cross-head 26 is carried by supports 52 and 54 on a base 56, and the movable cross-head 28 is carried by screws 58 and 60 which are actuated to draw the rock bolt '12 downwardly. In the downward movement of the rock bolt 12 the wedge 14 expands the elements 24 providing a gripping action simulating the gripping action between the expanding elements of the rock bolt and roof strata of the mine.

With this new and useful combination of elements it is possible to ascertain, in a laboratory, the safe load, proper torque, and breaking strains of mine rock bolts, so that the tension limit of mine roof strata bolts will not be exceeded, and failures in mine roofs will be reduced to a minimum.

With this testing apparatus bolt manufacturers may determine the correct amount of tensile stress for maximum bolting security, and then convert these tensile stress values to torque-wrench values for the various mine rock bolting conditions. Furthermore by the use of elongation or stress gauges, and a vertical or horizontal stationary fixture mine operators may be able to determine experimentally the correct amount of torque for a mine rock bolt.

It will be understood that geological cores, obtained by core drilling, may be used in place of, or in combination with the refractory materials.

With the parts assembled as illustrated and described the anchor assembly is mounted on the upper bearing plate on the upper cross-head and force is applied to the mine rock bolt 12 by drawing the lower cross-head downwardly. The tensile strength is determined by the point at which the anchor fails, such as by stripping the threads of the rock bolt, or by a rupture in the bolt, and with the tensile strength determined, the same tension may be applied to all rock bolts in the mine roof.

The indicating dial, electric motor for moving the cross-head, and mechanical structures that transfer the force to the indicating dial are positioned in a pit below the floor level.

With the mine rock bolt tester or anchor of this invention there are no moving parts during an anchor test. The parts are moved only after the test is completed, and even then the split sleeve is easily removed as the outer surface of the sleeve and inner surface of the outer casing are coated with grease or the like. In this operation a plug may be used to press the sleeve out of the outer casing.

When cylindrical geological cores having a vertical bore or hollow are available taken from natural rock strata, the testing procedure is similar but with the additional step of pouring a slurry or thin mixture of mortar and water between the outer surface of this natural core and the described split sleeves 18 and 20 after assembly in the outer casing 16.

The mortar upon setting fills all remaining spaces between the sleeves 18 and 20 and the casing 16 whereby test results are completely accurate.

This use of mortar may also be used to fill spaces which may occur when using the simulated rock 22 of refractory material. Material other than mortar may be used for this purpose provided that it set up near rock hard.

After testing a given mine bolt the parts are disassembled for inspection by pressing or pulling out the core 22 and split sleeves 18 and 20 together from the casing 16 in the same manner as pressing or pulling out bearings from machine parts. To assist in this, a light coating of grease or the like is first placed on the inner surface of the casing 16. The tensile testing machine as shown and described may be used for pressing out the said split sleeves and core from the casing 16 or an ordinary machine shop press may be used. It will be seen that the refractory material 22 can also be called an annular element of rock-like material. The bolt 12 extends in one direction yond the common ends of the casing 16,

sleeve 20 and element 22, such common ends being identified as those closest to the cross-head 26. The cross-head 26 and the bearing plate 30 together represent what can be called a frame means for engaging the common ends of the casing 16, sleeves 18 and 20, and element of rocklike material 22, preventing their movement in one direction, specifically, a downward direction.

The lower cross-head 28 with bolt head 32, washer 34, mine roof plate 36, and lower bearing plate 38 and screws 58 and 60, all together may be understood to form a means engageable with the end of the bolt 12 which is opposite to the end on which the expansion elements are positioned for pulling on the bolt 12 to test it.

From the foregoing description, it is thought to be obvious that a testing anchor for mine rock bolts constructed in accordance with by invention is particularly well adapted for use, by reason of the convenience and facility with which it may be assembled and operated, and it will also be obvious that my invention is susceptible of some change and modification without departing from the principles and spirit thereof, and for this reason I do not wish to be understood as limiting myself to the precise arrangement and formation of the several parts herein shown in carrying out my invention in practice, except as claimed.

What is claimed is:

1. A mine roof rock bolt tester comprising an elongated bolt, expansion elements on one end of the bolt, a casing positionable around said expansion elements, a split sleeve in said casing, refractory material positioned between said split sleeve and the expansion elements, a stationary cross-head upon which said casing, sleeve, refractory material, and expansion elements are positioned, a movable cross-head in which the end of the bolt opposite to the end on which the expansion elements are positioned is secured, and means for actuating the movable cross-head to determine the force required to rupture the rock bolt.

2. In a mine rock bolt, the combination which comprises an upper stationary cross-head, a lower movable cross-head positioned in alignment with said upper stationary cross-head, an outer casing positioned on and extended from said upper stationary cross-head, a split sleeve in said casing, a refractory material in said split sleeve, gripping elements designed to he threaded on a rock bolt and positioned to coact with said refactory material for retaining the rock bolt in said outer casing, and means urging said movable cross-head away from said stationary cross-head.

3. In a mine rock bolt tester, the combination which comprises, an upper stationary cross-head having an opening for a bolt therethrough, a lower movable crosshead also having an opening for a bolt therethrough, bearing plates on said cross-heads and positioned over the openings for bolts therethrough, an outer casing positioned on the bearing plate of the upper cross-head, a split sleeve positioned in said outer casing, a rock bolt extended through the bearing plates and cross-heads and positioned with the head thereof below the lower cross-head, gripping elements threaded on said bolt, wedge means for urging said gripping elements outwardly, a refractory material positioned between said gripping elements and split sleeve, and means for actuating the lower cross-head for providing tension in said rock bolt.

4. A mine rock bolt tester as described in claim 3, in which contacting surfaces of the split sleeve and outer casing are coated with grease. v

5. A mine rock bolt tester as described in claim 3, in which the cross-heads are provided with supports, and the supports of the movable cross-head are threaded and provided with operating nuts.

6. A mine roof rock bolt tester comprising an elongated bolt, expansion elements on one end of the bolt, a casing positioned around said expansion elements, a split sleeve in said casing, an annular element of rock- References Cited by the Examiner US. Bureau of Mines Report of Investigations, Report No. 5,649, Evaluating Anchorage Testing Methods for Expansion Type Mine Roof Bolts, 1960.

RICHARD C. QUEISSER, Primary Examiner. G. M. GRON, Assistant Examiner. 

6. A MINE ROOF ROCK BOLT TESTER COMPRISING AN ELONGATED BOLT, EXPANSION ELEMENTS ON ONE END OF THE BOLT, A CASING POSITIONED AROUND SAID EXPANSION ELEMENTS, A SPLIT SLEEVE IN SAID CASING, AN ANNULAR ELEMENT OF ROCKLIKE MATERIAL POSITIONED BETWEEN SAID SPLIT SLEEVE AND THE EXPANSION ELEMENTS, SAID BOLT EXTENDING IN ONE DIRECTION BEYOND COMMON ENDS OF SAID CASING, SLEEVE, AND SAID ELEMENT, A FRAME MEANS ENGAGING SAID CASING, SLEEVE AND SAID ELEMENT FOR PREVENTING THEIR MOVEMENT IN SAID ONE DIRECTION, AND MEANS ENGAGEABLE WITH THE END OF SAID BOLT OPPOSITE TO THE END OF WHICH SAID EXPANSION ELEMENTS ARE POSITIONED FOR PULLING ON SAID BOLT TO TEST SAID BOLT. 